Moving pictures captured on film may typically have a frame rate of 24 Hz, while NTSC (National Television System Committee) interlaced video may have a frame rate of 30 Hz and a corresponding interlaced field rate of 60 Hz, and PAL (Phase Alternating Lines) interlaced video may have a frame rate of 25 Hz and a corresponding interlaced field rate of 50 Hz. Interlaced video is video wherein a single image may be decomposed into two fields, a first field containing even numbered scan lines of the image and a second field containing odd numbered scan lines of the image. Therefore, to convert a sequence of moving pictures from film to NTSC interlaced video or PAL interlaced video, each frame of film may need to be converted into several interlaced fields. With NTSC interlaced video, frames of film may alternately be converted into three interlaced fields and two interlaced fields, while each frame of film may need to be converted into two interlaced fields for use with PAL interlaced video. This frame to frame conversion ratio may be referred to as film cadence. For NTSC, the film cadence is 3:2, while the film cadence is 2:2 for PAL. Other commonly encountered film cadences may include 5:5 or 4:4 for 12 Hz animation and 3:2:2 for sped up film.
Modern standard definition, extended definition, and high definition display systems may be progressive in nature, wherein an entire frame may be displayed in its entirety, rather than sequentially displaying a first interlaced field of a frame followed by a second interlaced field of a frame. Therefore, displaying interlaced video, such as NTSC interlaced video or PAL interlaced video, on a progressive display may require that the interlaced video be de-interlaced. De-interlacing doubles the number of scan lines present in an interlaced field. Modern de-interlacers may use techniques such as field jam, line interpolation, or combinations thereof to create a de-interlaced frame. Field jam combines two consecutive interlaced fields, such as an even interlaced field and an odd interlaced field, into a single de-interlaced field. Line interpolation creates new lines from existing lines in an interlaced field. Furthermore, if a film cadence is detected, the de-interlacer may be able to infer which adjacent interlaced fields were mastered from the same film frame and selectively combine the interlaced fields to recreate the original progressive frames.
However, due to editing of an interlaced video stream, such as during post production, it may be possible that the film cadence is broken. For example, commercials, music videos, and other media often contain breaks in the film cadence due to post production editing that occurs after moving pictures captured on film are converted to interlaced video. When the film cadence is broken, one or more interlaced fields may be missing from the film cadence. Therefore, if the de-interlacer continues to combine adjacent interlaced fields according to the expected film cadence, fields from different film frames may be combined and this may result in combing artifacts, which may be objectionable to the viewer.